Managing the light flux from a light emitting diode (LED) source, typically being a point source, requires the use of a complex optical lens for gathering as much of the light emitted from the source as possible and redirecting the light to a surface to be illuminated in the far field in a predetermined illumination pattern. Maximizing the efficiency of an LED lighting system is measured, in part, by the amount of light successfully captured and usefully redirected by the optics to a far field object. A typical LED source has a primary resin optic molded around and encapsulating the semiconductor such that the light emitted from the source ideally behaves similar to a point source having a cosine-like distribution centrally peaking along or near the forward central axis of the source and declining to a minimum at 90 degrees from the central axis. So as to direct the light to a specific surface in the far field distal to the source, a secondary illumination optic is required. The secondary illumination optic is arranged to capture the light emitted from the LED primary optic and redirect or focus the light on a far field surface.
Light emitted near the peak of the light distribution is emitted from the LED primary optic at relatively small angles from the central lens axis is suitable for capture by a conventional convex optical lens secondary optic wherein a light ray impinging on the incident surface of the secondary optic is refracted through the lens, refracted again at the exiting surface and directed on to a far field target surface. Light emitted from the LED primary lens at higher angles from the central axis escaping capture by a centrally positioned convex optical element can be gathered and redirected by a further lens element axially surrounding and contiguous to the LED primary lens. Because this peripheral light is emitted at high angles, the peripheral lens is often in the form of a minor constructed to reflect the light forward and onward to the far field surface. Alternatively, a total internal reflection (TIR) lens is constructed around the LED primary lens wherein the light is captured by a lens having an aspheric incident surface, shaped similar to a cylinder, designed to direct light from the LED source to a circumferentially positioned lens surface at angles so as to produce internal reflection at the respectively designed circumferentially positioned lens surface thereby directing the light forward and out through an exiting surface designed to refract the light on to the far field surface. In the afore described manner, the light flux capture from the LED source is maximized as all light, regardless of the angle from the central axis, is captured by a lens surface, redirected and passed on to a far field surface. Manipulation of the lens design can further be adjusted to form desired patterns or distributions on a far field object.
The combination secondary illumination lens having a central and surrounding TIR optic is known as a tulip type lens. As the optical pathways of the central convex lens and the outer internal reflection lens elements provide separate and distinct ray pathways, the lenses may be formed together as an integrated tulip lens assembly forming the secondary illumination optic. In order to accomplish the optical characteristics afore described, the central optic and the TIR optic of a tulip lens tends to be thick. Further, because of the complex nature of the surfaces of a tulip lens, injection molded resin optic lens construction techniques are desirable; however, lens resin optics having large surface to surface thicknesses, as required in prior art tulip type lenses, present a number of serious disadvantages.
Generally the cost of manufacturing an injection molded tulip type secondary illumination optic is high principally due to the mold cycle time resulting from the length of time required to cool and set a thick lens to a temperature permitting the release of the lens from the mold. Further, thick lens designs require enhanced molding techniques so as to avoid material shrinkage or other temperature gradient induced deformities during the manufacturing process thereby reducing yield rates. Generally, the lens thickness, as measured between a mold surface and an opposing mold surface, should be minimized. Best yield rates and lowest mold cycle times are achieved with a thin and consistent mold surface to opposing mold surface resin thicknesses so as to provide minimal resin utilization, homogeneous and rapid cooling, and minimal material shrinkage. The benefits of consistent resin thicknesses are maximized when the thermal flux, during the mold cool down, from the resin, to the mold surfaces is homogeneous throughout molded lens as the lens cools, thereby providing homogeneous cooling minimizing residual resin distortion.
Although the tulip type combination lens design is ideally suited as a highly efficient secondary illumination optic for LED sources, the manufacturing constraints and costs render the design less competitive in a highly competitive market place. What is needed is an improved secondary illumination optics lens that is commensurate with injection resin optic molding techniques and manufacturable at lower costs and higher yields.